1. Field of the Invention
The present invention relates to an ejection head, an image forming apparatus, and an ejection control method, and more particularly to the structure of an ejection head for ejecting droplets from an ejection nozzle, and to an ejection control technique.
2. Description of the Related Art
In recent years, inkjet printers have come to be used widely as data output apparatuses for outputting images, documents, or the like. An inkjet printer forms data on a printing matter (a recording medium) by driving recording elements (nozzles) of a recording head in accordance with data, thereby causing ink to be ejected from the nozzles.
In an inkjet printer, a print head having a plurality of nozzles is caused to move relative to the printed medium, and ink droplets are ejected from the nozzles, whereby the desired image is formed on the printed medium.
In an inkjet recording apparatus, when the ink inside the nozzles comes into contact with air, the ink solvent evaporates from the surface that is in contact with the air, and the viscosity of the ink increases. When ink is used whose viscosity is increased in this manner, nozzle obstruction occurs more easily, and failure to eject or ejection malfunction occurs.
At present, preliminary ejection (purging) is performed in order to prevent nozzle obstruction from occurring due to increased-viscosity ink, and applying suction to clogged  nozzles and other recovery operations are performed.
In the inkjet recording apparatus described in Japanese Patent Application Publication No. 8-142331, a configuration is adopted whereby aggregation of color material is optimally controlled by an aggregation device which causes the color material components dispersed in the solvent to aggregate inside the head, and an ejection device which causes the color material components that have aggregated separately from the aggregation device to be ejected.
In the image forming apparatus described in Japanese Patent Application Publication No. 2002-248766, a configuration is adopted in an inkjet recording apparatus which ejects ink in which charged particles are dispersed in a solvent using a piezo ejection-type head, whereby a particle distribution control device is provided which controls the distribution of particles in the ejection head, and the solvent carrier only is ejected using the particle distribution control device after image recording is completed or when in a cleaning mode.
In the inkjet printer device described in Japanese Patent Application Publication No. 9-57974, a configuration is adopted whereby an electrophoretic migration electrode which causes the color material particles of a pigment-based ink to concentrate at the ejection nozzle by electrophoretic migration, an ejection electrode which ejects the ink, and an OFF-time measurement device which measures the OFF time in which the ink is not being ejected are provided, and the voltage applied to the electrophoretic migration electrode is controlled according to the OFF time thus measured.
However, when preliminary ejection for preventing nozzle obstruction is performed frequently, the amount of ink ejected during preliminary ejection increases, and ink is wasted. It also becomes impossible to print during the preliminary ejection operation, which can lead to decreased productivity.
An object of the inkjet recording apparatus described in Japanese Patent Application Publication No. 8-142331 is to control the aggregation of charged particles (color material particles) and enhance the precision of the deposited droplet concentration, and no disclosure is made therein concerning nozzle and meniscus surface maintenance for adapting to evaporation of the ink solvent.
In the configuration adopted in the image forming apparatus described in Japanese Patent Application Publication No. 2002-248766, ejection of the solvent carrier is limited to being performed when image recording is completed, or during execution of a cleaning mode, and no disclosure is made therein concerning preliminary ejection during printing, or of preliminary ejection in anticipation of ejection problems.
An object of the inkjet printer device described in Japanese Patent Application Publication No. 9-57974 is ink concentration control whereby the time in which ejection is not performed is measured, the aggregation of color material is controlled, and the color material is ejected in stable fashion, and disclosure of a preliminary ejection or other recovery operation is not made in this publication.